Msg#: 4483872 posted 10:47 pm on Aug 15, 2012 (gmt 0)
Location would be marginal at best, as you often see with Google or other sites that note your IP address and try to GEO IP target you by looking up your IP address in known ranges for Internet Service Providers (ISP). Search for "ip location" or "ip geolocation" for further reading.
As far as OS and browser go, about all you can do is see if the user has opted to allow their user agent to be sent along with their request to your server and parse it for known patterns. The PHP superglobal $_SERVER['HTTP_USER_AGENT'] will be the value you will be targeting.